Developing rollers, known from U.S. Pat. No. 6,714,754, are used in an image forming apparatus for developing an electrostatic latent image on a surface of an image bearing member by use of a non magnetic toner to form a toner image. To obtain good images, the requirements of the developing roller are relatively high, especially with respect to the conductivity, hardness, uniformess of the surface etcetera. Furthermore it is important that the charge providing layer has a good connection to the base layer to prevent local separation or peeling off of the charge providing layer due to the friction between the charge providing layer and the particles of the non magnetic toner. A charge providing layer according to this patent contains conductive particles dispersed therein to have conductivity.
In the developing roller according to the above mentioned patent, an elastic intermediate layer is provided between the charge providing layer and the base layer in order to increase the adhesion between the base layer and the charge providing layer.
This prior art method has the disadvantage that an additional layer, e.g., the intermediate layer, is required on the developing roller. Such an intermediate layer often comprises a solvent having a good adherence to the base layer. Such solvent is not good for the environment. Furthermore, the electrical conductivity of such an elastic layer is relatively poor, which is detrimental for the functioning of the roller.
In EP 1 079 280 a charge providing layer is described, which layer is obtained by a coating containing filler particles; the size and amount of the filler particles determining the surface roughness of the resulting charge providing layer. A disadvantage of the use of such filler particles is firstly, that adhesion problems may occur with the baser layer and secondly that uneven distribution of the filler particle may lead to an uneven surface roughness, which is undesirable.